Evaluation of the effect of landfill leachate on surface and groundwater quality: a case study in tropical Sri Lanka using the evidence of stable isotopes.

The disposal of solid wastes is a significant problem in urban areas in many developed and developing countries. Waterways are often subjected to pollution by effluents discharged from solid waste dumpsites. The stable isotopes and water quality data provide useful information on tracing pollutant sources and their contaminant pathways. The effect of a major solid waste dumpsite on surface and groundwater quality of the surrounding area was investigated by measuring water quality parameters and stable isotopes of deuterium ( 2 H), oxygen ( 18 O), 15 N-ΝΟ 3 and 18 O-NO 3 in tropical Sri Lanka. The surface water and groundwater wells close to the dumpsite indicated clear evidence of leachate contamination with enriched total dissolved solids (TDS), total suspended solids (TSS), ammonia, biochemical oxygen demand (BOD 5 ) and Cl - levels. The correlation of groundwater quality parameters, i.e. EC (-r 2 = 0.8), TDS (-r 2 = 0.8), TSS (-r 2 = 0.5), ammonia (-r 2 = 0.4), phosphates (-0.6), sulphates (-0.5), Cl - (-0.6) and isotope δ 2 H‰ (-0.9) with distance from the dumpsite, further confirmed the effects of dumpsite on groundwater quality. The composition of δ 15 N-ΝΟ 3 and δ 18 O-NO 3 isotopes in the groundwater indicated that the dominant source of NO 3 - to groundwater is manure septic originating from the dumpsite. The findings of the study provided clear evidence of the effect of open dumping on the water resources of the surrounding area and the need for remedial measures.